Gowerpoint's uBook has always been one of the better tools to read e-books on a Windows Mobile device. It supports various formats natively, including more obscure stuff like CHM, RB, and unencrypted MobiPocket, has skinning support, and allows you to adjust fonts in uncountable ways.

Changelog of V0.9h beta:

First release candidate for uBook 1.0

Fixed Install

Fixed issues (and speed) with embedded RTF images

Remove Easy/Advance modes and replaced them by having +/- control for each section

Added Option to disable the file name at the top of a slideshow

Changed Auto-Text-Open to have a 3rd choice: open only when one text is in the zip file